If you need that much animation on a page to tell your story, isn't it a good sign that video might be more fit for purpose? Video was designed for storytelling, it will work on most devices, and it has well-established UI and conventions, such as a play button and progress bar.
If you're going to provide a play button in your scrollmation to automatically advance the action anyway, you've already recognised how irritating it is to manually page through an animated story by scrolling or swiping. So why then go to the trouble of creating a scroll-based animation that repurposes a 20+ year old convention and attempts to reinvent a tiny proportion of what video has to offer?
Is it just for the novelty value?
Is it because it makes you feel smarter?
How is it better for users trying to understand your story?
I'd love to hear from anyone who's considered both video and scrollmation and chosen the latter.